In the 3rd Generation Partnership Project (3GPP), which is a mobile communication system standardization project, the formulation of specifications of a Device to Device Proximity Service (D2D ProSe) is promoted.
As modes of the D2D ProSe, two modes including direct discovery and direct communication are defined.
Here, the direct discovery is a mode for searching for another radio terminal by directly transmitting, between radio terminals, a discovery signal without a specified specific destination. The direct communication is a mode for directly transmitting data between radio terminals by specifying a specific destination (destination group).